1. Field of the Invention
The present invention relates to a magnetic memory device which is provided with memory cells including magnetoresistive effect revealing bodies, and is configured such that information can be recorded thereon and read out therefrom.
2. Description of the Related Art
As the magnetic memory device of the above-mentioned kind, a magnetic memory device is known which is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2004-178623. This magnetic memory device is a magnetic random access memory (hereinafter also referred to as “MRAM”), in which a plurality of memory cells including a pair of magnetoresistive effect revealing bodies (magnetoresistive effect elements) and a pair of backflow-preventing diodes are two-dimensionally arranged.
In the magnetic memory device, an X direction current drive circuit as one write circuit included in an X direction current drive circuit group, and a Y direction current drive circuit as one write circuit included in a Y direction current drive circuit group are selected, whereby write currents are supplied to a write word line and a write bit line to which are connected the selected X direction current drive circuit and the selected Y direction current drive circuit, respectively. In this case, the write word line and the write bit line are composed of a pair of lines connected to each other on sides thereof remote from the X direction current drive circuit and the Y direction current drive circuit, whereby they are configured such that the write currents supplied from the respective current drive circuits are turned back on the remote sides for being returned to the respective current drive circuits. As a result, a synthetic magnetic field of the write currents is applied to a memory cell, which is disposed at an intersection of the write word line and the write bit line through which the write currents are flowing, out of the plurality of memory cells included in the memory cell group, whereby one of the pair of magnetoresistive effect revealing bodies in the memory cell assumes a high resistance value, and the other of the pair of magnetoresistive effect revealing bodies assumes a low resistance value, thereby storing one-bit information. In this case, the X direction current drive circuit and the Y direction current drive circuit are configured as illustrated in FIG. 5 of the publication.
On the other hand, in the above magnetic memory device, to read out information stored in one of the plurality of memory cells, a pair of transistors (column-selecting transistors) are operated via a Y direction address decoder shown in FIG. 9 of the publication, thereby making it possible to supply electric currents to a pair of sense bit lines (current supply lines) connected to the emitter terminals of the pair of column-selecting transistors, respectively, via current/voltage converting resistors. Further, if one constant current circuit is operated via an X direction address decoder, it becomes possible to introduce a constant current from a memory cell connected to one sense word line (current introducing line) connected to the constant current circuit. As a result, one memory cell, which is disposed at an intersection of the pair of current supply lines and the current introducing line and is connected to the current supply lines and the current introducing line, is selected, whereby electric currents dependent on the resistance values of the respective magnetoresistive effect revealing bodies flow through a first path from the power source to the ground via one of the current/voltage converting resistors, one of the column-selecting transistors, one of the magnetoresistive effect revealing bodies included in the selected memory cell, one of the backflow-preventing diodes, and the constant current circuit, and a second path from the power source to the ground via the other of the current/voltage converting resistors, the other of the column-selecting transistors, the other of the magnetoresistive effect revealing bodies included in the selected memory cell, the other of the backflow-preventing diodes, and the constant current circuit, respectively. Further, voltages proportional to the current values of electric currents flowing through the first and second paths are generated across opposite ends of the respective current/voltage converting resistors arranged in the paths. Therefore, by detecting voltages (or the difference in the voltages) generated in the respective current/voltage converting resistors, it is possible to detect the magnitudes of the resistance values of the respective magnetoresistive effect revealing bodies included in the selected memory cell, thereby reading out information stored in the memory cell.